Seat belts are used in automobiles to protect occupants during a collision. When a collision is detected or anticipated, a pretensioner can be used to take up slack and tighten against the occupant to a greater extent than it is under a normal use state.
The present invention relates to a seat belt retractor, a pretensioner thereof, and a method of tensioning a seat belt.
One aspect of the present invention is a seat belt retractor having a spool for tensioning a seat belt and a pretensioner.
Another aspect of the present invention is the pretensioner itself mentioned above. The pretensioner according to the present invention can include a stationary body, a pretensioner gear, a spool driving gear, and a pretensioner gear driving mechanism.
The pretensioner gear can be attached to the stationary body using a plurality of integrally formed breakable projections inserted into a plurality of complementary holes so that the pretensioner gear is immobilized relative to the stationary body. One of the pretensioner gear and the stationary body can have the integrally formed breakable projections and the other of the pretensioner gear and the stationary body can have the complementary holes. For example, the breakable projections can be integrally formed with the stationary body while the complementary holes can be formed on one side of the pretensioner gear.
The pretensioner gear, for example, can be a ring gear having outer teeth and inner teeth, and the spool driving gear, for example, also can be a ring gear having outer teeth and inner teeth. The spool can include a spool gear that engages the inner teeth of the spool driving gear.
The complementary holes can be blind holes to retain broken projections within the holes so that they do not fall out of the pretensioner gear. The stationary body and the projections, for example, can be formed of aluminum. The stationary body, for example, can be a cover.
The spool driving gear, which is adapted for rotating the spool, can be spaced and disengaged from the pretensioner gear so that the pretensioner gear does not interfere with normal operation of the spool.
The pretensioner gear driving mechanism is for engaging the pretensioner gear with the spool driving gear and driving the pretensioner gear to thereby rotate the spool. The pretensioner gear driving mechanism drives the pretensioner gear to break the projections and mobilize the pretensioner gear, engage the pretensioner gear with the spool driving gear, and drive the spool driving gear, which rotates the spool and tension the seat belt.
The pretensioner gear driving mechanism can include a conduit, balls, and a ball propelling mechanism. The conduit can have an opening and the pretensioner gear can be positioned adjacent to the opening so that part of the pretensioner gear extends into the opening. The balls are positioned inside the conduit for driving the pretensioner gear. The ball propelling mechanism can move the balls inside the conduit so that the balls force against the portion of the pretensioner gear extending into the opening to break the projections, engage the pretensioner gear with the spool driving gear, and rotate the spool driving gear to tension the seat belt.
The ball propelling mechanism can comprise a gas generator disposed at one end of the conduit and a piston situated inside the conduit. Activating the gas generator generates gas that propels the piston against the balls to drive the balls against the portion of the pretensioner gear extending into the opening. The balls engage the outer teeth of the pretensioner gear, and the outer teeth of the spool driving gear engage the inner teeth of the pretensioner gear to rotate the spool.
The projections can include first and second projections, with the first projection positioned closer to the opening through which a leading ball passes than the second projection so that the leading ball the conduit breaks the first projection first, and then breaks the second projection.
The second projection can be positioned away from the first projection so that when the first projection breaks, the pretensioner gear pivots about the second projection to cause the inner teeth of the pretensioner gear to engage the outer teeth of the spool driving gear away from a position at which the leading ball pushes the pretensioner gear. In this respect, the second projection can be spaced away from the first projection by at least a quarter of the circumferential distance of the pretensioner gear.
Another aspect of the present invention is a method of tensioning the seat belt in the seat belt retractor having the spool. The method can comprise the steps of providing the stationary body and the pretensioner gear, which can be attached to the stationary body with the integrally formed breakable projections inserted into the complementary holes so that the pretensioner gear is immobilized relative to the stationary body. Again, one of the pretensioner gear and the stationary gear can have the integrally formed breakable projections and the other of the pretensioner gear and the stationary body can have the complentary holes, with the projections inserted into the complementary holes. The method further comprises providing the spool driving gear for rotating the spool and positioning the spool driving gear spaced and disengaged from the pretensioner gear so that the pretensioner gear does not interfere with normal operation of the spool. The method also includes driving the pretensioner gear to break the projections and mobilize the pretensioner gear, engaging the pretensioner gear with the spool driving gear, and driving the spool driving gear to rotate the spool and tension the seat belt.
The pretensioner gear can be driven by providing the conduit provided with the opening and positioning the pretensioner gear adjacent to the opening so that part of the pretensioner gear extends into the opening. Balls are provided inside the conduit. Moving the balls against the portion of the pretensioner gear extending into the opening breaks the projections, engages the pretensioner gear with the spool driving gear, and rotates the spool driving gear to tension the seat belt.
The balls can be moved or propelled by providing the gas generator disposed at one end of the conduit and providing a piston situated inside the conduit. Activating the gas generator propels the piston against the balls.